The traditional method used to protect roofs from rain and other forms of inclement weather was to lay down several layers of material, normally felt soaked with bitumen, thereby building up a waterproof membrane. This method has several problems, two of which are that the process is very long, and it is also susceptible to contamination by rainwater or other foreign materials. Furthermore, the bitumen must be heated to the point where it gives off noxious odors.
In recent years, alternate systems using elastomeric membranes have become increasingly popular. A suitable elastomeric membrane is laid over the top surface of the roof itself or, more preferably, an insulation board. A variety of methods for fastening the elastomeric membrane to the surface of the roof have also been developed. One method is to spread an adhesive over the entire surface of the roof before laying down the membrane. This process is very labor-intensive and requires the installers to be exposed to adhesives that give off noxious fumes.
Alternatively, the membrane can be fastened to the roof mechanically. Several devices have been developed which require that a nail or screw be allowed to penetrate the membrane. This can lead to rips and tears in the membrane, especially as the membrane expands and contracts in response to changes in the ambient temperature. These breaches in the integrity of the membrane in turn can lead to water leakage and eventual damage to the underlying roof.
A variety of other devices have also been developed which are capable of securing a membrane to the upper surface of a roof without penetrating the membrane. The applicant believes that the following references are illustrative of the non-penetrating anchoring systems which have been patented. Included in the following list of references are patents related to screw guns. These are included for being related to, but not disclosing the applicant's fastener system.
______________________________________ U.S. Pat. No. Patentee ______________________________________ 4,519,175 Resan 4,617,771 Tomaszewski 4,624,092 Baginski 4,631,887 Francovitch 4,658,558 Verble 3,960,191 Murray 3,973,605 DeCaro 4,236,555 Dewey 4,246,939 Boegel 4,361,997 DeCaro 4,397,412 Dewey 4,638,532 Yang et al 4,657,167 Mays ______________________________________
U.S. Pat. No. 4,519,175 issued to Resan discloses a three-piece fastening apparatus wherein the roofing membrane is laid over the bottom piece and then a second tined piece is clipped over the membrane and the protruding boss of the bottom piece. The top piece of the device is then screwed onto the second piece thereby locking the device together and securing the membrane.
U.S. Pat. No. 4,617,771 issued to Tomaszewski discloses a three-piece fastening system which snaps together. The device includes an elastic ring which provides tension when a top piece is snapped into the bottom piece.
U.S. Pat. No. 4,624,092 issued to Baginski discloses a two-piece fastening system which snaps together. The bottom piece of the device serves as the male element; the membrane is laid over the bottom piece, and a collar is snapped over the top of the bottom piece. This device, however, allows the area of the membrane directly over the bottom piece to be exposed to the atmosphere.
U.S. Pat. No. 4,631,887 issued to Francovitch discloses a three-piece fastening system which snaps together. In the use of this device, a second piece is inserted inside of the bottom piece which helps maintain the tension produced when the top, or cap piece is snapped over the membrane and the protruding boss of the bottom piece.
U.S. Pat. No. 4,638,532 issued to Yang et al discloses an anchoring plate with a hinged retainer for securing a membrane to a roof surface. The membrane is held between the anchor plate and the retainer without penetration.
U.S. Pat. No. 4,658,558 issued to Verble discloses a two-piece fastening system which snaps together. In this device, the bottom piece serves as the female piece. The bottom piece is attached to the top surface of the roof, the membrane is laid out, and the top piece is snapped into the bottom piece, thereby locking the device together and securing the membrane.
U.S. Pat. No. 3,960,191 issued to Murray discloses a driving attachment for a portable power screwdriver capable of automatically feeding fasteners to the nosepiece.
U.S. Pat. No. 3,973,605 issued to DeCaro discloses a driving tool for threaded fasteners with a washer installed on the fastener shank. Fasteners are loaded manually into the tool and guided for straight insert into the workpiece.
U.S. Pat. No. 4,236,555 issued to Dewey discloses a screw gun for driving screws up to twelve inches long from a standing position, the tool having adjustments to accomodate screws of various lengths.
U.S. Pat. No. 4,246,939 issued to Boegel discloses a screw driving apparatus for driving screws with large washers over three inches in diameter, the driver designed for use on flat roofs to retain insulation.
U.S. Pat. No. 4,361,997 issued to DeCaro discloses a fastening screw with two sets of threads. The screw is used to fasten down a plate.
U.S. Pat. No. 4,397,412 issued to Dewey discloses a screw gun for long fasteners for attaching thick insulating boards to roofs, the screw gun having provision for preventing nails being loaded backwards.
U.S. Pat. No. 4,657,167 issued to Mays discloses a fastening machine for roof and deck coverings which includes a supply magazine.
Many of these devices are capable of securing an elastomeric membrane to the upper surface of a roof without penetrating the membrane; however, there are several limitations and suboptimizations inherent in these devices and the prior art in general.
First and foremost, the way in which previously-disclosed devices generate the restraining force necessary to secure the membrane to to roof creates problems. For example, devices which screw together, such as the device disclosed by Resan in U.S. Pat. No. 4,519,175, carry with them the danger that the device will be over-tightened, thereby straining or even ripping the membrane. Alternatively, devices which screw together may be under-tightened, allowing the top, or cap piece of the device to work its way loose.
Devices which utilize the thickness of the membrane itself to generate the majority of the restraining force used to hold the device together and, hence, anchor the membrane to the roof have other problems associated with their use. Devices such as those disclosed by Verble in U.S. Pat. No. 4,658,558 and Francovitch in U.S. Pat. No. 4,631,887, in essence, call for the installer to provide the wedging force necessary to either push a cap over a protruding boss as in the case of Francovitch, or to push a plug into a housing as in the case of Verble. These types of devices can stretch and fatigue the membrane, increasing the risk that a rip will form which will allow water to pass through the membrane and damage the underlying roof structure. Furthermore, fastening devices which employ the thickness of the membrane itself to supply the majority of the tensional force necessary to keep the device locked together have very little margin for error. For example, the calender seams formed where two sheets of the roofing membrane are joined together are often too thick to fit into these types of devices. This can lead to either the necessity for careful pre-planning of the placement of the devices, or wastage of those bottom pieces which are installed too near a calender seam. Also, devices of this type that utilize base plates which are basically circular may give rise to a large number of irregularly-distributed wrinkles which gives the impression of a slovenly installation.
A second major problem with the devices disclosed by the existing patents is the difficulty of servicing these devices. After an elastomeric membrane has been installed on a roof, it may become necessary to inspect the membrane for a variety of reasons; for example, when a water leak is discovered inside the underlying structure. With the previously-patented fasteners it is almost impossible to disassemble the fastening system without damaging both the device and the membrane.
The Yang et al reference has an anchor device and hinged retainer, but lacks an insert member to maintain a tight grip on the membrane. The Yang et al patent also uses a normal screw which is separate from the anchor plate, unlike the present invention.
Of the cited screw gun systems only Boegel and Mays show applying screws to any sort of rectangular plate or washer, the screws and plates starting out as separate. In the two devices cited above the screw has to be driven into the plate or washer by the screwgun. The DeCaro device shows a screw with an attached washer, but it is quite small and is not for the same purpose as the large plate disclosed by the applicant. The screw and anchoring plate of the applicant's device come as one unit from the start.